NiFe Layered-Double-Hydroxide Nanosheet Arrays on Graphite Felt: A 3D Electrocatalyst for Highly Efficient Water Oxidation in Alkaline Media

Energy-Efficient Co-production of Benzoquinone and H2 Using Waste Phenol in a Hybrid Alkali/Acid Flow Cell

In both the manufacturing and chemical industries, benzoquinone is a crucial chemical product. A perfect and economical method for making benzoquinone is the electrochemical oxidation of phenol, thanks to the traditional thermal catalytic oxidation of phenol process requires high cost, serious pollution and harsh reaction conditions. Here, a unique heterostructure electrocatalyst on nickel foam (NF) consisting of nickel sulfide and nickel oxide (Ni9S8-Ni15O16/NF) was produced, and this catalyst exhibited a low overpotential (1.35 V vs. RHE) and prominent selectivity (99 %) for electrochemical phenol oxidation reaction (EOP). Ni9S8-Ni15O16/NF is beneficial for lowering the reaction energy barrier and boosting reactivity in the EOP process according to density functional theory (DFT) calculations. Additionally, an alkali/acid hybrid flow cell was successfully established by connecting Ni9S8-Ni15O16/NF and commercial RuIr/Ti in series to catalyze phenol oxidation in an alkaline medium and hydrogen evolution in an acid medium, respectively. A cell voltage of only 0.60 V was applied to produce a current density of 10 mA cm-2. Meanwhile, the system continued to operate at 0.90 V for 12 days, showing remarkable long-term stability. The unique configuration of the acid-base hybrid flow cell electrolyzer provides valuable guidance for the efficient and environmentally friendly electrooxidation of phenol to benzoquinone.

Mesoporous hydrogel electrodes with flexible frameworks exhibiting enhanced mass transport for the oxygen evolution reaction

Mesoporous hydrogel electrodes with unique flexible mesopores surrounded by CoOOH nanosheets were prepared via the electrochemical deposition of hybrid cobalt hydroxide nanosheets, exhibiting high oxygen evolution reaction activity at a high current density owing to the enhanced mass transport of oxygen molecules.

A moderate method for in situ growing Fe-based LDHs on Ni foam for catalyzing the oxygen evolution reaction

Fe-based LDHs have been proven to be an excellent class of catalysts for the oxygen evolution reaction (OER). To achieve industrial applications of water splitting, it is critical to develop a cost-effective and simple strategy to achieve large-area catalytic electrodes. Herein, we present a moderate in situ method for growing Fe-based layered double hydroxide nanosheets on a Ni foam (LDH@NF) substrate at room temperature. Through systematic experimental design characterization, it is found that this in situ growth process is mainly driven by moderate oxidation of Fe2+ in an O2-dissolved solution, the consequent local alkaline environment, and abundant TM2+ ions (Ni2+, Co2+, Ni2+/Co2+). Compared with other in situ methods, this method is not accompanied by violent redox reactions and is favorable for the uniform growth of LDHs, and the composition of the catalyst can be easily regulated. Specifically, the optimized NiFe-LDH@NF catalyst demonstrates excellent catalytic performance in the alkaline water oxidation reaction with a low overpotential of 206/239 mV at a current density of 10/100 mA cm-2, respectively.

Branched Porous Ni3N as a Catalytic Electrode for Selective Semidehydrogenation of Tetrahydroisoquinoline

Oxygen evolution in electrochemical water splitting needs a high overpotential that significantly reduces the energy efficiency. To explore an alternative anodic reaction to promote the production of hydrogen at the other end of water splitting and at the same time to get high-value-added chemicals is highly desirable. Herein, we demonstrate a novel branched porous Ni3N catalyst that is prepared for dehydrogenation of tetrahydroisoquinoline, which acts as an anodic oxidation reaction to promote H2 formation on the other end. Interestingly, the Ni3N catalytic electrode can induce effective semidehydrogenation with the selective formation of dihydroisoquinoline, which is difficult to be obtained by the usual direct synthesis route. The catalytic electrode exhibits a low potential of 1.55 V (vs RHE) for a catalytic current density of 61 mA cm-2 with dehydrogenation of tetrahydroisoquinoline and hydrogen production. In situ Raman spectra studies suggest that NiOOH is formed on the electrode surface, which mediates the oxidation semidehydrogenation process. This work also provides a strategy to fabricate nitride materials for applications beyond selective semidehydrogenation of tetrahydroisoquinoline.

Coupling Glycerol Conversion with Hydrogen Production Using Alloyed Electrocatalysts

Herein, uniform precious alloys including PtAg, PdAg, and PtPdAg nanoparticles were synthesized as electrocatalysts for glycerol oxidation reaction (GOR). The structures of the samples were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectrometry. The catalytic performance of the samples was evaluated in both alkaline and acidic electrolytes. Among the samples, PtPdAg exhibited superior activity with the largest current density of 3.77 mA cm-2 in alkaline solutions, which is 4.1 and 7.7 times those of Pd/C and Pt/C, respectively. In acidic solutions, the PtPdAg catalyst shows the highest current density of 0.58 mA cm-2, which is 1.8 times that of the Pt/C catalyst. The products of GOR were analyzed by high-performance liquid chromatography. Eight products including oxalic acid, tartronic acid, glyoxylic acid, glyceric acid, glyceraldehyde (GLAD), glycolic acid, lactic acid, and dihydroxyacetone were detected. Notably, in acidic solutions, PtAg and PtPdAg yielded the largest GLAD selectivity of 92.2% at 0.6 and 0.8 V, respectively. Using the alloyed catalysts, electrolysis processes coupling the GOR with the hydrogen evolution reaction were conducted. The conversion of glycerol and production of hydrogen were determined. To highlight the energy efficiency, a solar-panel-powered electrolysis process was conducted for the simultaneous production of hydrogen and high-valued products.

NiFe-Coordination Polymers-Derived Layered Double Hydroxides as Bifunctional Materials: Effect of the Ni : Fe Ratio on the Electrochemical Performance

The development of an efficient and cost-effective material is highly desirable for electrochemical devices such as electrolyzers and supercapacitors. Especially, pseudomorphic transformations of metal-organic frameworks (MOFs)/coordination polymers (CPs) into layered double hydroxides (LDHs) materials endow well-defined porosities, high surface area, exchangeable interlayer anions and easily adjustable electronic structure that are truly required for oxygen evolution reaction (OER) and high-performance supercapacitor applications. Herein, we have prepared NiFe-LDHs of various Ni/Fe ratios via a facile room-temperature alkaline hydrolysis of NiFe-CPs precursors. Electrochemical studies reveal that the catalyst having high amount of Fe (Ni1.2 Fe1 -LDH) showed the better OER activity with a low Tafel slope (65 mV dec-1 ) in 1 M KOH. On the other hand, the catalyst containing higher amount of Ni with better layered structure (Ni11.7 Fe1 -LDH) showed high performance for supercapacitor (702 F g-1 at 0.25 A g-1 ) in 3 M KOH. Moreover, a solid-state asymmetric supercapacitor device Ni11.7 Fe1 -LDH/AC was fabricated which exhibited a specific capacitance of 18 F g-1 at a current density of 1 A g-1 . The device displayed high cycling stability with 88% of capacitance retention after 7000 cycles. The experimental findings in this work will help in the futuristic development of NiFe-LDH based electrocatalysts for the enhanced electrochemical performances.

Improved Electrochemical Alkaline Seawater Oxidation over Cobalt Carbonate Hydroxide Nanowire Array by Iron Doping

Constructing efficient and low-cost oxygen evolution reaction (OER) catalysts operating in seawater is essential for green hydrogen production but remains a great challenge. In this study, we report an iron doped cobalt carbonate hydroxide nanowire array on nickel foam (Fe-CoCH/NF) as a high-efficiency OER electrocatalyst. In alkaline seawater, such Fe-CoCH/NF demands an overpotential of 387 mV to drive 500 mA cm^-2, superior to that of CoCH/NF (597 mV). Moreover, it achieves excellent electrochemical and structural stability in alkaline seawater.

Facile formation of Zn-incorporated NiFe layered double hydroxide as highly-efficient oxygen evolution catalyst

Electrochemical water splitting is the primary method to produce green hydrogen, which is considered an efficient alternative to fossil fuels for achieving carbon neutrality. For meeting the increasing market demand for green hydrogen, high-efficiency, low-cost, and large-scale electrocatalysts are crucial. In this study, we report a simple spontaneous corrosion and cyclic voltammetry (CV) activation method to fabricate Zn-incorporated NiFe layered double hydroxide (LDH) on commercial NiFe foam, which shows excellent oxygen evolution reaction (OER) performance. The electrocatalyst achieves an overpotential of 565 mV and outstanding stability of up to 112 h at 400 mA cm^-2. The active layer for OER is shown to be β-NiFeOOH according to the results of in-situ Raman. Our findings suggest that the NiFe foam treated by simple spontaneous corrosion has promising industrial applications as a highly efficient OER catalyst.

Improved Alkaline Seawater Splitting of NiS Nanosheets by Iron Doping

Seawater electrolysis driven by renewable electricity is deemed a promising and sustainable strategy for green hydrogen production, but it is still formidably challenging. Here, we report an iron-doped NiS nanosheet array on Ni foam (Fe-NiS/NF) as a high-performance and stable seawater splitting electrocatalyst. Such Fe-NiS/NF catalyst needs overpotentials of only 420 and 270 mV at 1000 mA cm^-2 for the oxygen evolution reaction and hydrogen evolution reaction in alkaline seawater, respectively. Furthermore, its two-electrode electrolyzer needs a cell voltage of 1.88 V for 1000 mA cm^-2 with 50 h of long-term electrochemical durability in alkaline seawater. Additionally, in situ electrochemical Raman and infrared spectroscopy were employed to detect the reconstitution process of NiOOH and the generation of oxygen intermediates under reaction conditions.

One-Step High-Temperature Electrodeposition of Fe-Based Films as Efficient Water Oxidation Catalysts

Electrolysis of water to produce hydrogen requires an efficient catalyst preferably made of cheap and abundant metal ions for the improved water oxidation reaction. An Fe-based film has been deposited in a single step by electrochemical deposition at temperatures higher than the room temperature. Until now, the electrodeposition of iron oxide has been carried out at 298 K or at lower temperatures under a controlled atmosphere to prohibit atmospheric oxidation of Fe²⁺ of the iron precursor. A metal inorganic complex, ferrocene, and non-aqueous electrolyte medium propylene carbonate have been used to achieve electrodeposition of iron oxide without the need of any inert or controlled atmosphere. At 298 K, the amorphous film was formed, whereas at 313 K and at higher temperatures, the hematite film was grown, as confirmed by X-ray diffraction. The transformation of iron of the ferrocene into a higher oxidation state under the experimental conditions used was further confirmed by X-ray photoelectron spectroscopy, ultraviolet-visible, and electron paramagnetic resonance spectroscopic methods. The films deposited at 313 K showed the best performance for water oxidation with remarkable long-term electrocatalytic stability and an impressive turnover frequency of 0.028 s^-1 which was 4.5 times higher than that of films deposited at 298 K (0.006 s^-1). The observed overpotential to achieve a current density of 10 mA cm^-2 was found to be 100 mV less for the film deposited at 313 K compared to room-temperature-derived films under similar experimental conditions. Furthermore, electrochemical impedance data revealed that films obtained at 313 K have the least charge transfer resistance (114 Ω) among all, supporting the most efficient electron transport in the film. To the best of our knowledge, this is the first-ever report where the crystalline iron-based film has been shown to be electrodeposited without any post-deposition additional treatment for alkaline oxygen evolution reaction application.

NiFe-based electrocatalyst anchored on nanocone with tip-field effect for improved oxygen evolution reaction

The development of high efficiency oxygen evolution electrocatalyst is of great significance for water splitting reaction. Herein, an efficient cone-structured NiFe-LDH/Nicone/Ti catalyst is fabricated by electrodeposition method towards enhanced oxygen evolution reaction (OER). The featured tip curvature of nanocone structure can accelerate the reaction kinetics of OER by offering a field-enhanced aggregation of local hydroxide ion reactant on the catalyst surface, and thus improves the performance of the NiFe catalyst. Accordingly, NiFe-LDH/Nicone/Ti requires only a low overpotential of 292 mV to achieve 50 mA cm^-2, and with high stability under continuous high-current operations. In addition, the alkali-electrolyzer using NiFe-LDH/Nicone/Ti electrode exhibits good performance with a voltage of 1.73 V at 50 mA cm^-2and displays excellent stability in long-term stability test. This cone-structured catalyst design with field-enhanced local hydroxide ion aggregation effect provides a promising method for the development of highly active OER electrocatalysts.

Ce-Modified Flowerlike NiFe-MOF Nanostructure Based on Ion Competitive Coordination for Enhancing the Oxygen Evolution Reaction

Metal-organic framework (MOF) has become a popular electrocatalyst for the oxygen evolution reaction (OER) because of its large specific surface area and adjustable porosity. Nevertheless, the electrochemical performance of MOFs has been greatly limited by poor intrinsic conductivity and catalytic activity. Herein, we report a Ce-doped nanoflower-like MOF material Ce@NiFe-MOF-5 via a facile ion competitive coordination effect and doping method. Benefiting from the nanoflower structure formed by the stacking of nanosheets, a large number of active sites can be exposed, which favors electron/mass transfer during water oxidation. The coordination substitution of Ce ions not only promoted an increase in the number of active sites on the surface of the nanosheets but also optimized the electronic structure of pristine NiFe-MOF. The well-designed Ce@NiFe-MOF-5 catalysts exhibited superior OER performance under basic conditions, which only required an overpotential of 258 mV at a current density of 10 mA cm^-2 and a Tafel slope of 54.44 mV dec^-1. Moreover, when Ce@NiFe-MOF-5 served as an anode and Pt/C as a cathode, the two-electrode system only needed 1.56 V to drive overall water splitting at 10 mA cm^-2.

Crystalline-Dependent Discharge Process of Locally Enhanced Electrooxidation Activity on Ni2P

The state-of-the-art transition-based electrocatalysts in alkaline media generally suffer from unavoidable surface reconstruction during oxygen evolution reaction measurements, leading to the collapse and loss of the crystalline matrix. Low potential discharge offers a gentle way for surface reconstruction and thus realizes the manipulation of the real active site. Nevertheless, the absence of a fundamental understanding focus on this discharge region renders the functional phase, either the crystalline or amorphous matrix, for the controllable reconstruction still undecidable. Herein, we report a scenario to employ different crystalline matrices as electrocatalysts for discharge region reconstruction. The representative low crystalline Ni₂P (LC-Ni₂P) possesses a relatively weak surface structure compared with highly crystalline or amorphous Ni₂P (HC-Ni₂P or A-Ni₂P), which contributes abundant oxygen vacancies after the discharge process. The fast discharge behavior of LC-Ni₂P leads to the uniform distribution of these vacancies and thus endows the inner interface with reactant activating functionality. A high increase in current density of 36.7% is achieved at 2.32 V (vs RHE) for the LC-Ni₂P electrode. The understanding of the discharge behavior in this study, on different crystalline matrices, presents insights into the establishment of controllable surface reconstruction for an effective oxygen evolution reaction.

FTIR-Assisted Electroreduction of CO2 and H2O to CO and H2 by Electrochemically Deposited Copper on Oxidized Graphite Felt

Obtaining CO and H₂ from electrochemical CO₂ reduction (CO₂RR) offers a viable alternative to reduce CO₂ emissions and produce chemicals and fuels. Herein, we report a simple strategy for obtaining polycrystalline copper deposited on oxidized graphite felt (Cu-OGF) and its performance on the selective conversion of CO₂ and H₂O to CO and H₂. For the electrode obtaining, graphite felt (GF) was first oxidized (OGF) in order to make the substrate hydrophilic and then copper particles were electrochemically deposited onto OGF. The pH of deposition was investigated, and the CO₂RR activity was assessed for the prepared electrodes at each pH (2.0, 4.0, 6.0, 8.0, and 10.0). It was found that pH 2.0 was the most promising for CO₂RR due to the presence of hexagonal copper microparticles. Fourier transform infrared analysis of the produced gases showed that this is a low-cost catalyst capable of reducing CO₂ and H₂O to CO and H₂, with Faradaic efficiencies between 0.50 and 5.21% for CO and 50.87 to 98.30% for H₂, depending on the experimental conditions. Hence, it is possible for this gas mixture to be used as a fuel gas or to be enriched with CO for use in Fischer-Tropsch processes.

Optimized Mo-doped IrOx anode for efficient degradation of refractory sulfadiazine

Electrochemical advanced oxidation processes (EAOPs) is considered to be an efficacious method to degrade antibiotics. However, the performance of the anode has become the main limiting factor of this technology. In this study, due to the electron-deficient characteristics and the improvement of OER performance of Mo, we chose to use thermal decomposition to incorporate Mo into IrO2 to prepare anodes with industrial applicability. Under the optimal ratio of Ir to Mo is 7:3, (Ir0.7Mo0.3)Ox electrode's particular pore structure can expose more active sites and create a channel for the transportation of electrons, thereby promoting the formation of free radicals and degrading pollutants more efficiently. (Ir0.7Mo0.3)Ox electrode also has a higher mass activity (6.332 A g-1, three times that of the IrO2 electrode) and a larger electrochemical active area (ECSA, 375.43 cm2, seven times that of the IrO2 electrode). In addition, the optimal conditions of (Ir0.7Mo0.3)Ox electrode for degrading sulfadiazine(SDZ) were explored, which achieved a higher removal than traditional electrodes (90% removal within 4 h) when the Ti plate was the substrate. Through the intermediate products of SDZ degradation and related literatures, two possible degradation pathways of SDZ were speculated. This research provides a new type of anode catalyst for the degradation of sulfonamide antibiotics, which is possible for industrial application.

Amorphous Co-Mo-B Film: A High-Active Electrocatalyst for Hydrogen Generation in Alkaline Seawater

The development of efficient electrochemical seawater splitting catalysts for large-scale hydrogen production is of great importance. In this work, we report an amorphous Co-Mo-B film on Ni foam (Co-Mo-B/NF) via a facile one-step electrodeposition process. Such amorphous Co-Mo-B/NF possesses superior activity with a small overpotential of 199 mV at 100 mA cm-2 for a hydrogen evolution reaction in alkaline seawater. Notably, Co-Mo-B/NF also maintains excellent stability for at least 24 h under alkaline seawater electrolysis.

Enhanced Electrochemical Water Oxidation Activity by Structural Engineered Prussian Blue Analogue/rGO Heterostructure

Prussian blue analogue (PBA), with a three-dimensional open skeleton and abundant unsaturated surface coordination atoms, attracts extensive research interest in electrochemical energy-related fields due to facile preparation, low cost, and adjustable components. However, it remains a challenge to directly employ PBA as an electrocatalyst for water splitting owing to their poor charge transport ability and electrochemical stability. Herein, the PBA/rGO heterostructure is constructed based on structural engineering. Graphene not only improves the charge transfer efficiency of the compound material but also provides confined growth sites for PBA. Furthermore, the charge transfer interaction between the heterostructure interfaces facilitates the electrocatalytic oxygen evolution reaction of the composite, which is confirmed by the results of the electrochemical measurements. The overpotential of the PBA/rGO material is only 331.5 mV at a current density of 30 mA cm⁻² in 1.0 M KOH electrolyte with a small Tafel slope of 57.9 mV dec⁻¹, and the compound material exhibits high durability lasting for 40 h.

Co, Mn co-doped Fe9S11@Ni9S8 supported on nickel foam as a high efficiency electrocatalyst for the oxygen evolution reaction and urea oxidation reaction

The Earth's fossil resources will be exhausted soon, so it is urgent to find clean and efficient new energy for replacing fossil resources. Hydrogen energy is gradually attracting the attention of the public and electrolysis of water is considered to be one of the important means of hydrogen production because of its simplicity and convenience. In this paper, a hydrothermal method for the synthesis of a Co and Mn co-doped bimetallic sulfide Fe₉S₁₁@Ni₉S₈ electrocatalyst is proposed for the first time. The prepared Co-Mn-Fe₉S₁₁@Ni₉S₈/NF electrocatalyst exhibits excellent electrocatalytic activity for the oxygen evolution reaction (OER) and urea oxidation reaction (UOR). It can provide a current density of 10 mA cm^-2 with only 193 mV overpotential for the OER and a current density of 10 mA cm^-2 with only 1.33 V potential for the UOR, which are far superior to those of most reported electrocatalysts. What is noteworthy is that the unique nanoflower structure of Co-Mn-Fe₉S₁₁@Ni₉S₈/NF increases the specific surface area of the material and the introduction of Co and Mn ions promotes the formation of high valence state Ni and Fe and enhances the charge transfer rate. The density functional theory (DFT) calculation shows that the in situ generated Co-Mn-Fe-NiOOH material derived from Co-Mn-Fe₉S₁₁@Ni₉S₈ exhibits the best water adsorption energy and the best electrical conductivity, thus improving the catalytic performance of the material. This work provided a new idea for the development of bimetallic cation doped electrocatalysts with high efficiency and low cost.

Vertically growing nanowall-like N-doped NiP/NF electrocatalysts for the oxygen evolution reaction

Developing low-cost, high-performance and corrosion-resistant catalysts for water splitting is anticipated, but it will also be a big challenge. In this study, nanowall-like N-Ni₅P₄/Ni₂P/NF (N-NiP/NF) was synthesized by a simple two-step method involving hydrothermal treatment and phosphorylation. The catalyst has good catalytic activity for the OER, and only 160 mV is required to achieve a current density of 10 mA cm^-2 in 1 M KOH, which is even better than RuO₂, with good corrosion resistance. In addition, N-Co₂P/Ni₂P/NF (N-CoP/NF) was synthesized by the same method with good electrocatalytic properties and good conductivity towards the HER. N-NiP/NF was used as the anode and N-CoP/NF was used as the cathode to form the N-NiP//N-CoP double electrode system, which showed excellent electrolytic performance for water splitting, requiring only 1.48 V to reach 10 mA cm^-2. This is mainly due to the strong electronegativity of N that makes the N doping induce the electron transfer process, which results in a high catalytic activity of the adjacent transition metal atoms and thus promotes the electrolysis of water, as well as the unique vertical nanowall-like structure, which gives the material a large surface area and accessibility to active sites, facilitating the adsorption of water molecules and catalytic reactions. In addition, the unique structure favors the diffusion of water molecules and the release of gaseous products, ensuring close contact between the catalyst and the electroactive material. This simple non-metallic N doping strategy provides a new way to produce efficient non-precious metal catalysts.

Synergistic effect of oxidation etching and phase transformation triggered by controllable ion-bath microenvironments toward constructing ultra-thin porous nanosheets for accelerated industrial water splitting at high current density

Precisely tailoring the structure of inorganic materials at the micron and nanometer scales, especially in collaboration with component customization to design efficient, stable and low-cost transition-metal-based catalysts for industrial electrocatalytic water splitting (EWS) is a key renewable energy technology, but still facing a daunting challenge. Here, the controllable escape of Ni atom is adopted to disturb the hydrothermal ion-bath environment, thereby resulting in the coexistence of high valence Ni and Fe ions. Combined with a one-step hydrothermal coordination strategy, the timeline-adjusted ion-bath microenvironment can effectively trigger the phase transformation of carbonate hydroxide hydrate nanosheets (NFCH) to nickel ferrite intercalated NFCH ultra-thin porous nanosheets (NF-CH-O). Thanks to the high-energy phase boundary synergistic effect and the rapid mass transfer advantages of ultra-thin porous nanostructures, the as-prepared NF-CH-O nanosheets exhibit remarkable oxygen and hydrogen evolution reaction (OER/HER) catalytic activity and stability, with low overpotentials of 207/191 mV at 50 mA cm^-2, respectively, as well as the activity retention for 100 h. The alkaline water electrolyzer set up with NF-CH-O as both anodic and cathodic electrodes only requires a cell potential of 1.688 V to reach 50 mA cm^-2 in a continuous operation of 100 h. More impressively, NF-CH-O only requires overpotentials of 266, 292 mV and 1.877 V to drive high current densities up to 500 mA cm^-2 for OER, HER and EWS, respectively, and exhibits excellent stability with a reduction in the activity of less than 10% over cycles of more than 65 h. This work highlights the room-temperature controllable ion-bath oxidative etching strategy to design efficient bifunctional catalysts with ultra-thin porous structure and high-current-density activity. Meanwhile, combined with the advantages of direct growth on the substrate for mass production, such meticulous consideration of nanostructured design will be more competitive in the H₂-production industry.

Feasibility of Nickel–Aluminum Complex Hydroxides for Recovering Tungsten Ions from Aqueous Media

In this study, the adsorption and/or desorption capacity of tungsten ions using nickel–aluminum complex hydroxides was assessed. Nickel–aluminum complex hydroxides at various molar ratios, such as NA11 were prepared, and the adsorption capacity of tungsten ions was evaluated. Precisely, the effect of temperature, contact time, pH, and coexistence on the adsorption of tungsten ions in the water layer was demonstrated. Among the nickel–aluminum complex hydroxides at various molar ratios, the adsorption capacity onto NA11 was the highest of all adsorbents. The sulfate ions in the interlayer of NA11 was exchanged to tungsten ions, that is, the adsorption mechanism was ion exchange under our experimental conditions. Additionally, to elucidate the adsorption mechanism in detail, the elemental distribution and X-ray photoelectron spectroscopy of the NA11 surface were analyzed. Finally, the results indicated that the tungsten ions adsorbed using NA11 could be desorbed (recovered) from NA11 using sodium hydroxide solution. These results serve as useful information regarding the adsorption and recovery of tungsten ions using nickel–aluminum complex hydroxides from aqueous media.

Novel FeNi-Based Nanowires Network Catalyst Involving Hydrophilic Channel for Oxygen Evolution Reaction

Developing novel, efficient, and low-cost 3D FeNi-based oxygen evolution reaction (OER) catalysts with the special hydrophilic channel is still a challenge for improving hydrogen production efficiency. Herein, a novel 3D ethoxy substituted FeNi oxalate (ENWs-FeNi-C₂ O₄ ) nanowires network catalyst with hydrophilic channels is reported firstly, which shows an outstanding OER activity with a low overpotential (215 mV at 10 mA cm^-2 ) and small Tafel slope (54.5 mV dec^-1 ). OER catalytic mechanism indicates that the OH adsorption step and O₂ bubble diffusion step of OER reaction process can be significantly improved due to the special hydrophilic channels, and the ethoxy as an interlayer ligand not only expands the interlayer distance of layered FeNi (oxy) hydroxide true active species but modulates its electronic structure, promoting the *OOH formation step, and thus exhibiting the outstanding OER performance. This work provides a novel idea for the preparation of novel and efficient OER electro-catalysts with special 3D structures.

Boosting the Electrocatalytic Activity of Nickel-Iron Layered Double Hydroxide for the Oxygen Evolution Reaction byTerephthalic Acid

The development of a new type of oxygen evolution reaction (OER) catalyst to reduce the energy loss in the process of water electrolysis is of great significance to the realization of the industrialization of hydrogen energy storage. Herein, we report the catalysts of NiFe double-layer hydroxide (NiFe-LDH) mixed with different equivalent terephthalic acid (TPA), synthesized by the hydrothermal method. The catalyst synthesized with the use of the precursor solution containing one equivalent of TPA shows the best performance with the current density of 2 mA cm−2 at an overpotential of 270 mV, the Tafel slope of 40 mV dec−1, and excellent stable electrocatalytic performance for OER. These catalysts were characterized in a variety of methods. X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), and Raman spectrum proved the presence of TPA in the catalysts. The lamellar structure and the uniform distribution of Ni and Fe in the catalysts were observed by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). In X-ray photoelectron spectroscopy (XPS) of NiFe-LDH with and without TPA, the changes in the peak positions of Ni and Fe spectra indicate strong electronic interactions between TPA and Ni and Fe atoms. These results suggest that a certain amount of TPA can boost catalytic activity.

Enhanced electrocatalytic activity of FeNi alloy quantum dot-decorated cobalt carbonate hydroxide nanosword arrays for effective overall water splitting

The development of earth-abundant catalysts toward high-efficiency overall water splitting is of critical importance for electrochemical hydrogen production. Here, novel FeNi alloy quantum dot (QD)-decorated cobalt carbonate hydroxide (CoCH) nanosword arrays were successfully constructed on Ni foam (FeNi/CoCH/Ni foam) and used as an efficient bifunctional electrocatalyst for overall water splitting in alkaline media. Benefiting from the synergistic effect between the FeNi alloy QDs and CoCH, the FeNi/CoCH/Ni foam electrode delivers a current density of 20 mA cm^-2 at an overpotential of 240 mV and a small Tafel slope of 44.8 mV dec^-1 for the oxygen evolution reaction (OER). Further, it displays excellent performance for overall water splitting with a voltage of 1.49 V at 10 mA cm^-2 and maintains its activity for at least 23 h. In particular, it only needs low cell voltages of 1.54 and 1.6 V to drive high current densities of 100 and 400 mA cm^-2, respectively, which is much better than commercial Pt/C/Ni foam‖RuO₂/Ni foam, providing great potential for large-scale application.

A Superior and Stable Electrocatalytic Oxygen Evolution Reaction by One-Dimensional FeCoP Colloidal Nanostructures

Transition metal phosphides (TMPs) are expected to be excellent electrocatalysts for oxygen evolution reaction (OER) because of their high stability, highly conducting metalloid nature, highly abundant constituting elements, and the ability to act as a precatalyst due to in situ surface-formed oxy-hydroxide species. Herein, a "one-pot" colloidal approach has been used to develop a rod-shaped one-dimensional non-noble metal FeCoP electrocatalyst, which exhibits an excellent OER activity with an exceptionally high current density of 950 mA cm^-2, a turnover frequency value of 7.43 s^-1, and a low Tafel slope value of 54 mV dec^-1. The FeCoP electrocatalyst affords OER ultralow overpotentials of 230 and 260 mV at current densities of 50 and 100 mA cm^-2, respectively, in 1.0 M KOH, and demonstrates a superior catalytic stability of 10,000 cycles and durability up to 60 h at 50 mA cm^-2. An insight into the superior and stable electrocatalytic OER performance by the FeCoP nanorods is obtained by extensive X-ray photoelectron spectroscopy, X-ray diffraction, Raman and infrared spectroscopy, and cyclic voltammetry analyses for a mechanistic study. This reveals that a high number of electrocatalytically active sites enhance the oxygen evolution and kinetics by offering metal ion sites for utilitarian in situ surface formation and adsorption of *O, *OH, and *OOH reactive species for OER catalysis.

Carbon nanotube Encapsulated Metal selenide Nanostructures for Efficient Electrocatalytic Oxygen Evolution Reaction

Nickel selenide nanowires were grown inside carbon nanotubes through in situ encapsulation via one-step chemical vapor deposition. These NiSe2@CNT nanohybrids showed excellent electrocatalytic activity for water splitting with low overpotential...

Amorphous-crystalline FeNi2S4@NiFe-LDH nanograsses by molten salt as an industrially promising electrocatalyst for oxygen evolution

Inexpensive and accessible NiFe-based oxygen evolution reaction (OER) electrocatalyst are limited for practical industrial applications by its activity and stability under industrial conditions. Herein, FeNi2S4@NiFe-LDH heterostructure is constructed by molten...

Ce-Substituted Spinel CuCo2O4 Quantum Dots with High Oxygen Vacancies and Greatly Improved Electrocatalytic Activity for Oxygen Evolution Reaction

Exploring effective electrocatalysts for oxygen evolution reaction (OER) is a crucial requirement of many energy storage and transformation systems, involving fuel cells, water electrolysis, and metal-air batteries. Transition-metal oxides (TMOs) have attracted much attention to OER catalysts because of their earth abundance, tunable electronic properties, and so forth. Defect engineering is a general and the most important strategy to tune the electronic structure and control size, and thus improve their intrinsic activities. Herein, OER performance on spinel CuCo₂O₄ was greatly enhanced through cation substitution and size reduction. Ce-substituted spinel CuCe_δCo_2-δO_x (δ = 0.45, 0.5 and 0.55) nanoparticles in the quantum dot scale (2-8 nm) were synthesized using a simple and facile phase-transfer coprecipitation strategy. The as-prepared samples were highly dispersed and have displayed a low overpotential of 294 mV at 10 mA·cm^-2 and a Tafel slope of 57.5 mV·dec^-1, which outperform commercial RuO₂ and the most high-performance analogous catalysts reported. The experimental and calculated results all confirm that Ce substitution with an appropriate content can produce rich oxygen vacancies, tune intermediate absorption, consequently lower the energy barrier of the determining step, and greatly enhance the OER activity of the catalysts. This work not only provides advanced OER catalysts but also opens a general avenue to understand the structure-activity relationship of pristine TMO catalysts deeply in the quantum dot scale and the rational design of more efficient OER catalysts.

Iron-Facilitated Transformation of Mesoporous Spinel Nanosheets into Oxyhydroxide Active Species in the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is critical for many clean energy conversion and storage technologies because it contributes the electrons required for converting renewable electricity into value-added chemicals. Electrocatalysts can promote the sluggish oxygen evolution process involving four-electron transfer. Herein, we prepare mesoporous spinel oxide nanosheets and develop an efficient strategy using Fe substitution to enable mesoporous NiCo₂O₄ nanosheets to generate superior active centers for the OER. Additionally, the iron substitution also promotes the preoxidation of Co/Ni and facilitates the formation of active species. Raman spectroscopy data reveal that the active species of mesoporous NiCo₂O₄ nanosheets for the OER is NiCo₂O₄ itself, and the active species of Fe substitution in NiCo₂O₄ nanosheets are Ni(Co) oxyhydroxides. Therefore, the iron substitution is beneficial to facilitate the transformation of spinel NiCo₂O₄ into active Ni(Co) oxyhydroxides under OER conditions. Owing to the mesoporous nanosheet structure and the formation of oxyhydroxide active species, the optimized mesoporous Fe_0.2Ni_0.8Co₂O₄ nanosheet catalyst exhibits a low overpotential of 270 mV to deliver a current density of 10 mA cm^-2 and a small Tafel slope of 39 mV dec^-1 for the oxygen evolution reaction in alkaline media.

Optimization of Oxygen Evolution Reaction with Electroless Deposited Ni-P Catalytic Nanocoating

The low efficiency of water electrolysis mostly arises from the thermodynamic uphill oxygen evolution reaction. The efficiency can be greatly improved by rationally designing low-cost and efficient oxygen evolution anode materials. Herein, we report the synthesis of Ni-P alloys adopting a facile electroless plating method under mild conditions on nickel substrates. The relationship between the Ni-P properties and catalytic activity allowed us to define the best conditions for the electroless synthesis of highperformance Ni-P catalysts. Indeed, the electrochemical investigations indicated an increased catalytic response by reducing the thickness and Ni/P ratio in the alloy. Furthermore, the Ni-P catalysts with optimized size and composition deposited on Ni foam exposed more active sites for the oxygen evolution reaction, yielding a current density of 10 mA cm-2 at an overpotential as low as 335 mV, exhibiting charge transfer resistances of only a few ohms and a remarkable turnover frequency (TOF) value of 0.62 s-1 at 350 mV. The present study provides an advancement in the control of the electroless synthetic approach for the design and large-scale application of high-performance metal phosphide catalysts for electrochemical water splitting.